Log Message:
Updated package to latest version, 3.1.0, which includes some
infrastructure changes as well (packages for glib, react and ssl support
have been split off). Upstream changes include:

===== 3.1.0 (2017-07-19) =====

====== Additions ======

  * Port to Jbuilder (#374, Andrew Ray).
  * Lwt_io.establish_server_with_client_address (#346, Rudi Grinberg).
  * Lwt_unix.getcwd (#403, Rapha?l Proust).

====== Planned to break in 4.0.0 ======

  * Delete lwt.simple-top (#371).
  * Delete Lwt_chan (#441).

====== Fixes ======

  * Make Lwt_log functions tail-recursive (#348, Jan Doms).
  * Make more of Lwt_list tail-recursive (#347, Jan Doms).
  * Improve string messages in exceptions (#368, #382, Jan Doms, Rapha?l
    Proust).
  * Don't call Unix.set_nonblock or Unix.clear_nonblock unnecessarily on
    some fds (#356, David Sheets).
  * Lwt_unix.sleep and Lwt_unix.timeout returning too early when using
    libev (#433, Stijn Devriendt).
  * Lwt_sequence.fold_r iterating the wrong way in some cases (#405,
    Stijn Devriendt).
  * Build conflicts in some cases due to duplicate cst_to_constr
    function (#362, J?r?mie Dimino).
  * Don't use deprecated readdir_r system call (#430, Rapha?l Proust).

====== Miscellaneous ======

  * The Lwt core, lwt.ml, has been thoroughly refactored and commented
    (#354, reviewed Gabriel Radanne, Edwin T?r?k, Rapha?l Proust, Jan
    Doms, Fabian Hemmer, Sebastien Mondet, Simon Cruanes, Anil
    Madhavapeddy, Pierre Chambart, and many others).
  * Lots of tests for most of the Lwt core (#339, #389, #392, #440,
    #448, #450, Joseph Thomas, Ryan Slade).
  * Documentation fixes (including by Joseph Thomas, Rapha?l Proust,
    Richard Degenne, Stavros Polymenis).
  * Contributing documentation (#379).
  * Massively adjust whitespace for legibility (#400, #409, #416,
    Richard Degenne).
  * Improvements to CI (Etienne Millon, Raphael Rafatpanah, Zack Coker,
    Yotam Barnoy).
  * The additional packages lwt_ssl, lwt_react, lwt_glib get new minor
    releases, the change being new Jbuilder build systems (#374, Andrew
    Ray).

===== 3.0.0 (2017-04-10) =====

====== Breaking ======

  * These changes were originally announced in release 2.7.0 (#308).
  * Lwt_engine.libev now has an optional argument for selecting the libev back
    end (#269, #294, Jeremy Yallop).
  * Lwt_io.establish_server has been changed to make it more difficult to leak
    file descriptors (#258, #260).
  * Lwt_io.shutdown_server now evaluates to a promise, which completes when the
    listening socket's close(2) operation completes (#259).
  * Lwt_unix.bind now evaluates to a promise, because the bind(2) system call
    can block for Unix domain sockets (#296, requested David Sheets).
  * ocamlfind packages lwt.react, lwt.ssl, lwt.glib are replaced by lwt_react,
    lwt_ssl, lwt_glib. These have been separate OPAM packages, under those
names, since 2.7.0 (#301).